Emit method reference lambdas without helper method #9022
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SethTisue
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adriaanm
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lrytz
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maybe add some tests around serialization, ensure that the generated $deserializeLambda$ works as intended?
src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala
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viktorklang
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LGTM!
I guess t8549.scala failing is OK / expected?
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Under -Ydelambdafy:method-ref, when a lambda is just invoking a method (i.e. is "just a method reference"), such as `foo()` or `x => bar(x)`, then rather than emit an `invokedynamic` to a helper method that invokes the target method, emit an `invokedynamic` to the target method directly.
retronym
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| val lambdaTarget = originalTarget.attachments.get[JustMethodReference].map(_.lambdaTarget).getOrElse(originalTarget) | ||
| def asmType(sym: Symbol) = classBTypeFromSymbol(sym).toASMType | ||
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| val isInterface = lambdaTarget.owner.isTrait |
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@dwijnand This needs to be generalized to isTraitOrInterface now that lambda implementation methods may be owned by Java interfaces.
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Removing the release-notes label as this is still experimental and not something that most users would need. |
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Under -Ydelambdafy:method-ref, when a lambda is just invoking a method
(i.e. is "just a method reference"), such as
foo()orx => bar(x),(and other caveats around specialisation, boxing concerns for primitives
and its value classes, arrays, etc) then rather than emit an
invokedynamicto a helper method that invokes the target method, emitan
invokedynamicto the target method directly.$deserializeLambda$works as intendedExplanation
Note that this is opt-in, with
-Ydelambdafy:method-ref. The reason it's opt-in is because there's an assumption (an "invariant") in serialisation: if you serialise the lambda from one version of some code (v1) then deserialising it in a later version (v2) should run the new (v2) behaviour.For example, if you serialise the lambda
(x => x.toString())then deserialise it when the code is(x => x.toString().toUpperCase()), then the result should be upper-cased. Under-Ydelambdafy:method-refthe deserialised lambda will continue to just be a reference to Object'stoStringmethod. Also worth mentioning that in the same example, but with the versions swapped, the lambda will be a reference an$anonfun$...method that no longer exists in v2... which means that it will throw aLinkageErrorat runtime.